Angiotensin-converting enzyme from rabbit pulmonary vascular endothelial membranes will be characterized with respect to its polypeptide, oligosaccharide and heavy metal moieties. Antibodies directed against the pure holoenzyme and Fab fragments of these antibodies will be tested in vivo for their ability to inhibit the vasopressor response to angiotensin I and to prevent initiation and development of renin-dependent hypertension in animal models. The holoenzyme will be cleaved into defined fragments by chemical and enzymatic procedures. The peptide and oligosaccharide moieties of these fragments will be characterized and the fragments will be used as immunoadsorbants for selecting out antibodies directed against specific regions of the enzyme molecule. These antibodies may be useful in identifying the active site of the enzyme and in establishing its topography within the vascular endothelial membrane.